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Détail de l'auteur
Auteur J. Xu
Documents disponibles écrits par cet auteur
Affiner la rechercheEffects of SRB on cathodic protection of Q235 steel in soils / C. Sun in Materials and corrosion, Vol. 61 N° 9 (Septembre 2010)
in Materials and corrosion > Vol. 61 N° 9 (Septembre 2010) . - pp. 762–767
Titre : Effects of SRB on cathodic protection of Q235 steel in soils Type de document : texte imprimé Auteurs : C. Sun, Auteur ; J. Xu, Auteur ; F.H. Wang, Auteur Année de publication : 2011 Article en page(s) : pp. 762–767 Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Cathodic protection;Q235 steel; soils; SRB Résumé : The effects of sulfate reducing bacteria (SRB) on cathodic protection (CP) of the Q235 steel in the soils have been studied by bacterial analyses, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). The results showed that the pH value of the soil around the steel gradually increased, the number of SRB and the corrosion rate of the steel decreased, and the CP efficiency increased with the increasing of applied cathodic potential. At the cathodic polarization potential of −1050 mV, SRB still survived in the soils. At the same potential, the CP efficiency in the soil without SRB was higher than that with SRB, and the corrosion rate of the steel in the soil with SRB was much higher than that without SRB. The cathodic current density applied for the steel in the soil with SRB was bigger than that without SRB at the same cathodic potential. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.200905339/abstract [article] Effects of SRB on cathodic protection of Q235 steel in soils [texte imprimé] / C. Sun, Auteur ; J. Xu, Auteur ; F.H. Wang, Auteur . - 2011 . - pp. 762–767.
Génie mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 61 N° 9 (Septembre 2010) . - pp. 762–767
Mots-clés : Cathodic protection;Q235 steel; soils; SRB Résumé : The effects of sulfate reducing bacteria (SRB) on cathodic protection (CP) of the Q235 steel in the soils have been studied by bacterial analyses, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). The results showed that the pH value of the soil around the steel gradually increased, the number of SRB and the corrosion rate of the steel decreased, and the CP efficiency increased with the increasing of applied cathodic potential. At the cathodic polarization potential of −1050 mV, SRB still survived in the soils. At the same potential, the CP efficiency in the soil without SRB was higher than that with SRB, and the corrosion rate of the steel in the soil with SRB was much higher than that without SRB. The cathodic current density applied for the steel in the soil with SRB was bigger than that without SRB at the same cathodic potential. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.200905339/abstract
in Canadian geotechnical journal > Vol. 46 N° 9 (Septembre 2009) . - pp. 1062–1076
Titre : Effects of wetting–drying and stress ratio on anisotropic stiffness of an unsaturated soil at very small strains Type de document : texte imprimé Auteurs : C. W.W. Ng, Auteur ; J. Xu, Auteur ; S. Y. Yung, Auteur Article en page(s) : pp. 1062–1076 Note générale : Sciences de la Terre Langues : Anglais (eng) Mots-clés : Stiffness anisotropy Very small strain shear modulus Unsaturated Completely decomposed tuff Wetting–drying Stress ratio Rigidité anisotrope Module de cisaillement à très faibles déformations Non saturé Tuff complètement décomposé Mouillage–drainage Ratio des contraintes Index. décimale : 550 Sciences auxiliaires de la géologie. Résumé : The very small strain shear modulus of soil, G0, is affected by many factors including soil properties, current stress state, stress history, and matric suction. Very little research has been conducted on anisotropic shear moduli of unsaturated soils. In this study, the effects of wetting–drying and stress ratio on anisotropic shear stiffness of an unsaturated completely decomposed tuff (CDT) at very small strains have been investigated using a modified triaxial testing system equipped with three pairs of bender elements. During drying and wetting tests, the measured very small strain shear moduli increased in a nonlinear fashion, but at a reduced rate as the matric suction increased. Similar to the stress-dependent soil-water characteristic curves (SDSWCCs), there was hysteresis between the drying and wetting curves showing the variations in shear moduli with matric suction. Variation in suction on the specimens under isotropic conditions produced changes in stiffness anisotropy (expressed as G0(hh)/G0(hv)) together with anisotropic strains. In shearing tests at constant suctions, significant stress-induced stiffness anisotropy was observed due to a change in the stress ratio. While shearing at a constant stress ratio, G0(hh)/G0(hv) appeared to be constant.
Le module de cisaillement à très faibles déformations du sol, G0, est affecté par plusieurs facteurs, dont les propriétés du sol, l’état actuel des contraintes, l’historique des contraintes et la succion matricielle. Très peu de recherches ont été effectuées sur les modules de cisaillement anisotropes de sols non saturés. Dans cette étude, les effets du mouillage-drainage et du ratio des contraintes sur la rigidité en cisaillement anisotrope d’un sol non saturé de tuff complètement décomposé (TCD) à très faibles déformations ont été évalués à l’aide d’un système d’essai triaxial modifié qui était pourvu de trois paires d’éléments piézocéramiques. Durant les essais en drainage et en mouillage, le module de cisaillement à faibles déformations mesuré a augmenté de façon linéaire mais à un taux qui diminue selon l’augmentation de la succion matricielle. Il y avait des effets d’hystérésis entre les courbes en mouillage et en drainage montrant les variations des modules de cisaillement selon la succion matricielle, de façon semblable aux courbes caractéristiques sol-eau dépendantes des contraintes. Des variations de succion sur les échantillons soumis à des conditions isotropes ont causé des variations de rigidité anisotrope (exprimé G0(hh)/G0(hv)) combinées à des déformations anisotropes. Durant les essais en cisaillement à succion constante, de la rigidité anisotrope induite par les contraintes a été observée, due au changement du ratio des contraintes. Pendant le cisaillement à un ratio de contraintes constant, G0(hh)/G0(hv ) semble demeurer constant.
DEWEY : 550 ISSN : 0008-3674 En ligne : http://rparticle.web-p.cisti.nrc.ca/rparticle/AbstractTemplateServlet?calyLang=f [...] [article] Effects of wetting–drying and stress ratio on anisotropic stiffness of an unsaturated soil at very small strains [texte imprimé] / C. W.W. Ng, Auteur ; J. Xu, Auteur ; S. Y. Yung, Auteur . - pp. 1062–1076.
Sciences de la Terre
Langues : Anglais (eng)
in Canadian geotechnical journal > Vol. 46 N° 9 (Septembre 2009) . - pp. 1062–1076
Mots-clés : Stiffness anisotropy Very small strain shear modulus Unsaturated Completely decomposed tuff Wetting–drying Stress ratio Rigidité anisotrope Module de cisaillement à très faibles déformations Non saturé Tuff complètement décomposé Mouillage–drainage Ratio des contraintes Index. décimale : 550 Sciences auxiliaires de la géologie. Résumé : The very small strain shear modulus of soil, G0, is affected by many factors including soil properties, current stress state, stress history, and matric suction. Very little research has been conducted on anisotropic shear moduli of unsaturated soils. In this study, the effects of wetting–drying and stress ratio on anisotropic shear stiffness of an unsaturated completely decomposed tuff (CDT) at very small strains have been investigated using a modified triaxial testing system equipped with three pairs of bender elements. During drying and wetting tests, the measured very small strain shear moduli increased in a nonlinear fashion, but at a reduced rate as the matric suction increased. Similar to the stress-dependent soil-water characteristic curves (SDSWCCs), there was hysteresis between the drying and wetting curves showing the variations in shear moduli with matric suction. Variation in suction on the specimens under isotropic conditions produced changes in stiffness anisotropy (expressed as G0(hh)/G0(hv)) together with anisotropic strains. In shearing tests at constant suctions, significant stress-induced stiffness anisotropy was observed due to a change in the stress ratio. While shearing at a constant stress ratio, G0(hh)/G0(hv) appeared to be constant.
Le module de cisaillement à très faibles déformations du sol, G0, est affecté par plusieurs facteurs, dont les propriétés du sol, l’état actuel des contraintes, l’historique des contraintes et la succion matricielle. Très peu de recherches ont été effectuées sur les modules de cisaillement anisotropes de sols non saturés. Dans cette étude, les effets du mouillage-drainage et du ratio des contraintes sur la rigidité en cisaillement anisotrope d’un sol non saturé de tuff complètement décomposé (TCD) à très faibles déformations ont été évalués à l’aide d’un système d’essai triaxial modifié qui était pourvu de trois paires d’éléments piézocéramiques. Durant les essais en drainage et en mouillage, le module de cisaillement à faibles déformations mesuré a augmenté de façon linéaire mais à un taux qui diminue selon l’augmentation de la succion matricielle. Il y avait des effets d’hystérésis entre les courbes en mouillage et en drainage montrant les variations des modules de cisaillement selon la succion matricielle, de façon semblable aux courbes caractéristiques sol-eau dépendantes des contraintes. Des variations de succion sur les échantillons soumis à des conditions isotropes ont causé des variations de rigidité anisotrope (exprimé G0(hh)/G0(hv)) combinées à des déformations anisotropes. Durant les essais en cisaillement à succion constante, de la rigidité anisotrope induite par les contraintes a été observée, due au changement du ratio des contraintes. Pendant le cisaillement à un ratio de contraintes constant, G0(hh)/G0(hv ) semble demeurer constant.
DEWEY : 550 ISSN : 0008-3674 En ligne : http://rparticle.web-p.cisti.nrc.ca/rparticle/AbstractTemplateServlet?calyLang=f [...]
in Materials and corrosion > Vol. 61 N° 1 (Janvier 2010) . - pp. 7–15
Titre : Erosion–corrosion characteristic of nano-particulates reinforced Ni–Cr–Mo–Cu surface alloying layer in acidic flow and acidic slurry flow Type de document : texte imprimé Auteurs : J. Xu, Auteur ; C. Zhuo, Auteur Année de publication : 2010 Article en page(s) : pp. 7–15 Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Composite alloying layer; EIS; erosion–corrosion behavior; nano-particle reinforced; potentiodynamic polarization Résumé : In order to improve the corrosion and erosion–corrosion resistance of 316L stainless steel in engineering application, two kinds of composite alloying layers were prepared by a duplex treatment, consisting of Ni/nano-SiC and Ni/nano-SiO2 predeposited by brush plating, respectively, and a subsequent surface alloying with Ni–Cr–Mo–Cu by double glow process. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were performed on the two kinds of composite alloying layer using 10 wt% HCl solution to assess the corrosion behavior. Erosion–corrosion tests were carried out by erosion–corrosion test rig in acidic flow and acidic slurry flow for test time of 20 h at four different rotational speeds. Results of electrochemical tests indicated that the corrosion resistance of composite alloying layer with brush plating Ni/nano-SiO2 particles interlayer approximated to that of single Ni-based alloying layer, whereas the corrosion resistance of the composite alloying layer with brush plating Ni/nano-SiC particles interlayer was apparently inferior to that of Ni-based alloying layer in 10 wt% HCl solution at static state. Under the conditions of acidic flow and acidic slurry flow, the mass losses of tested samples increased with increase in the time of erosion–corrosion tests and the rotational speeds of samples. The mass losses of composite alloying layer with brush plating Ni/nano-SiO2 particles interlayer were lower than that of single Ni-based alloying layer at all rotational speeds, except at 1.88 m/s in acidic flow. The mass losses of composite alloying layer with brush plating Ni/nano-SiC particles interlayer were higher than that of single Ni-based alloying layer at all rotational speeds, but were obviously lower than that of AISI 316L stainless steel. The influences of second phase on the corrosion and erosion–corrosion of the two kinds of composite alloying layer were discussed in this paper. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.200905235/abstract [article] Erosion–corrosion characteristic of nano-particulates reinforced Ni–Cr–Mo–Cu surface alloying layer in acidic flow and acidic slurry flow [texte imprimé] / J. Xu, Auteur ; C. Zhuo, Auteur . - 2010 . - pp. 7–15.
Génie mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 61 N° 1 (Janvier 2010) . - pp. 7–15
Mots-clés : Composite alloying layer; EIS; erosion–corrosion behavior; nano-particle reinforced; potentiodynamic polarization Résumé : In order to improve the corrosion and erosion–corrosion resistance of 316L stainless steel in engineering application, two kinds of composite alloying layers were prepared by a duplex treatment, consisting of Ni/nano-SiC and Ni/nano-SiO2 predeposited by brush plating, respectively, and a subsequent surface alloying with Ni–Cr–Mo–Cu by double glow process. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were performed on the two kinds of composite alloying layer using 10 wt% HCl solution to assess the corrosion behavior. Erosion–corrosion tests were carried out by erosion–corrosion test rig in acidic flow and acidic slurry flow for test time of 20 h at four different rotational speeds. Results of electrochemical tests indicated that the corrosion resistance of composite alloying layer with brush plating Ni/nano-SiO2 particles interlayer approximated to that of single Ni-based alloying layer, whereas the corrosion resistance of the composite alloying layer with brush plating Ni/nano-SiC particles interlayer was apparently inferior to that of Ni-based alloying layer in 10 wt% HCl solution at static state. Under the conditions of acidic flow and acidic slurry flow, the mass losses of tested samples increased with increase in the time of erosion–corrosion tests and the rotational speeds of samples. The mass losses of composite alloying layer with brush plating Ni/nano-SiO2 particles interlayer were lower than that of single Ni-based alloying layer at all rotational speeds, except at 1.88 m/s in acidic flow. The mass losses of composite alloying layer with brush plating Ni/nano-SiC particles interlayer were higher than that of single Ni-based alloying layer at all rotational speeds, but were obviously lower than that of AISI 316L stainless steel. The influences of second phase on the corrosion and erosion–corrosion of the two kinds of composite alloying layer were discussed in this paper. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.200905235/abstract
in Materials and corrosion > Vol. 61 N° 9 (Septembre 2010) . - pp. 802–809
Titre : Influence of N,N′-dimethylaminoethanol as an inhibitor on the chloride threshold level for corrosion of steel reinforcement Type de document : texte imprimé Auteurs : J. Xu, Auteur ; L. Jiang, Auteur ; F. Xing, Auteur Année de publication : 2011 Article en page(s) : pp. 802–809 Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Chloride threshold level; concrete; inhibitor; N,N′-dimethylaminoethanol; steel reinforcement Résumé : The aim of this study is to examine the influence of N,N′-dimethylaminoethanol (DMEA) as an inhibitor on the chloride threshold level for corrosion of steel in a concrete contaminated by chlorides. The experiment has been carried out in a saturated Ca(OH)2 solution and chloride contaminated concrete containing different chloride and DMEA level. The critical point of corrosion onset is concluded by combining the open-circuit potential (Ecorr) with corrosion current (Icorr), which is decided by electrochemical impedance spectra (EIS) in the solution. Besides, the EIS has also been applied to determinate the chloride threshold level in the chloride contaminated concrete. It has been found that the presence of DMEA represented as an amino-alcohol inhibitor, exerts little influence on the chloride threshold level for corrosion of steel in the solution. Similarly, the effect of the DMEA on the chloride threshold level in the chloride contaminated concrete, is also negligible. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.200905393/abstract [article] Influence of N,N′-dimethylaminoethanol as an inhibitor on the chloride threshold level for corrosion of steel reinforcement [texte imprimé] / J. Xu, Auteur ; L. Jiang, Auteur ; F. Xing, Auteur . - 2011 . - pp. 802–809.
Génie mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 61 N° 9 (Septembre 2010) . - pp. 802–809
Mots-clés : Chloride threshold level; concrete; inhibitor; N,N′-dimethylaminoethanol; steel reinforcement Résumé : The aim of this study is to examine the influence of N,N′-dimethylaminoethanol (DMEA) as an inhibitor on the chloride threshold level for corrosion of steel in a concrete contaminated by chlorides. The experiment has been carried out in a saturated Ca(OH)2 solution and chloride contaminated concrete containing different chloride and DMEA level. The critical point of corrosion onset is concluded by combining the open-circuit potential (Ecorr) with corrosion current (Icorr), which is decided by electrochemical impedance spectra (EIS) in the solution. Besides, the EIS has also been applied to determinate the chloride threshold level in the chloride contaminated concrete. It has been found that the presence of DMEA represented as an amino-alcohol inhibitor, exerts little influence on the chloride threshold level for corrosion of steel in the solution. Similarly, the effect of the DMEA on the chloride threshold level in the chloride contaminated concrete, is also negligible. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.200905393/abstract
in Journal of the operational research society (JORS) > Vol. 63 N° 11 (Novembre 2012) . - pp. 1479–1491
Titre : Minimization of the k-th maximum and its application on LMS regression and VaR optimization Type de document : texte imprimé Auteurs : X. Huang, Auteur ; J. Xu, Auteur ; Wang, S., Auteur Année de publication : 2012 Article en page(s) : pp. 1479–1491 Note générale : operational research Langues : Anglais (eng) Mots-clés : piecewise linear optimization; least median of squares; value-at-risk Index. décimale : 001.424 Résumé : Motivated by two important problems, the least median of squares (LMS) regression and value-at-risk (VaR) optimization, this paper considers the problem of minimizing the k-th maximum for linear functions. For this study, a sufficient and necessary condition of local optimality is given. From this condition and other properties, we propose an algorithm that uses linear programming technique. The algorithm is assessed on real data sets and the experiments for LMS regression and VaR optimization both show its effectiveness. DEWEY : 001.424 ISSN : 0160-5682 En ligne : http://www.palgrave-journals.com/jors/journal/v63/n11/abs/jors2011163a.html [article] Minimization of the k-th maximum and its application on LMS regression and VaR optimization [texte imprimé] / X. Huang, Auteur ; J. Xu, Auteur ; Wang, S., Auteur . - 2012 . - pp. 1479–1491.
operational research
Langues : Anglais (eng)
in Journal of the operational research society (JORS) > Vol. 63 N° 11 (Novembre 2012) . - pp. 1479–1491
Mots-clés : piecewise linear optimization; least median of squares; value-at-risk Index. décimale : 001.424 Résumé : Motivated by two important problems, the least median of squares (LMS) regression and value-at-risk (VaR) optimization, this paper considers the problem of minimizing the k-th maximum for linear functions. For this study, a sufficient and necessary condition of local optimality is given. From this condition and other properties, we propose an algorithm that uses linear programming technique. The algorithm is assessed on real data sets and the experiments for LMS regression and VaR optimization both show its effectiveness. DEWEY : 001.424 ISSN : 0160-5682 En ligne : http://www.palgrave-journals.com/jors/journal/v63/n11/abs/jors2011163a.html
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